Atropine is a competitive muscarinic acetylcholine receptor antagonist. It is a naturally occurring tropane alkaloid extracted from deadly nightshade (Atropa belladonna), Jimson weed (Datura stramonium), mandrake (Mandragora officinarum) and other plants of the family Solanaceae. It is on the World Health Organization's List of Essential Medicines, a list of the most important medications needed in a basic health system.